Pseudomonas aeruginosa (P. aeurginosa) is a common opportunistic pathogen which causes bacterial keratitis, especially in contact lens usage (25,000-30,000 cases annually with treatment estimated at $15-30 million). The goal of the studies proposed is to determine the mechanisms involved in development of bacterial keratitis, especially the role of high mobility group box 1 (HMGB1), a prototypic alarmin. HMGB1 is a member of a family of danger associated molecular patterns (DAMPS), a mediator of the systemic inflammatory response syndrome, is elevated late in bacterial infection/sepsis and considered a target for disease treatment. Given that it is important in innate immunity, has different functions dependent on cellular localization, and has the ability to bind to Toll-like-receptors (TLR) and other molecules such as receptor for advanced glycation end products (RAGE), we hypothesize and provide preliminary supportive data, that it has significant amplification effects on the corneal inflammatory cell response and is an important therapeutic target in P. aeruginosa keratitis. Experiments described in this competitive renewal are a logical segue from the currently funded studies on TLR4, as we will focus on HMGB1, a molecule which interacts with TLR ligands and cytokines and activates cells through multiple surface receptors including TLR2, 4 and RAGE. Although HMGB1 is a well- studied member of a family of DAMPS, no information on its role in the infected cornea is available. Thus, how HMGB1 may set the stage, amplify the host immune response and is a target for treatment, will be determined in P. aeruginosa corneal infection. Two aims are proposed. Specific Aim 1: Will test the hypothesis that HMGB1 amplifies corneal inflammation and modulates the effector function of resident and infiltrating cells in bacterial keratitis. Specific Aim 2: Will test the hypothesisthat HMGB1 is a novel target for treatment and has clinical relevancy. The work is of relevance to human health and has considerable medical and economic impact.